436 PHYSIOLOGICAL CHEMISTRY. 



The solution may also be evaporated to dryness with or without sugar at a 

 temperature not exceeding 40 C. (104 F.), and the dry pepsin tested by the 

 directions given in Experiment 62. 



Clinical examination of gastric juice. The chemical examina- 

 tion of gastric juice, or of contents of stomach, is now considered of 

 great importance in the diagnosis of diseases of the stomach. The 

 juice for examination is obtained as follows : On an empty stomach, 

 the patient partakes of a test-meal, consisting usually of bread and 

 water, and an hour after or later (depending upon the form of meal 

 administered), the contents of the meal are withdrawn by means of a 

 stomach-tube. The liquid is filtered and used for further examina- 

 tions. These examinations consist of the following determinations : 

 a. Keaction ; b. presence of free acids ; c. presence of free hydro- 

 chloric acid ; d. presence of lactic and other organic acids ; e . total 

 acidity ; f. estimation of free hydrochloric acid ; g. presence of pepsin 

 and pepsinogen ; h. presence of rennet ferment and rennet zymogen ; 

 i. detection of proteids ; j. detection of carbohydrates. 



a. Reaction. This should be, and in all normal juices is, distinctly 

 acid to litmus paper. 



b. Free acids. The presence of free acids is detected by congo- 

 paper. This paper is prepared by soaking unsized paper in a 1 per 

 cent, aqueous solution of congo-red, and drying. If a drop of juice 

 is placed upon the paper, the presence of free acids is indicated by 

 the change of color from red to blue ; if the blue color is intense, 

 free hydrochloric acid is present. (Acid salts, such as acid phos- 

 phates, do not act on congo-red.) 



c. Free hydrochloric acid. There are a number of reagents for 

 the detection of free hydrochloric acid. The more important of 

 these are : methyl-violet, tropseolin 0, phloroglucin-vanillin, and 

 resorcin. 



Methyl-violet. If a concentrated aqueous solution of methyl-violet 

 is prepared and added to gastric juice containing free hydrochloric 

 acid, a change from violet to blue is at once noted. 



Tropceolin 0. Dissolved in alcohol the brownish-yellow solution 

 of tropseolin (diphenylamine-orange) is changed to a brown-red 

 or deep-red color upon the addition of juice containing free hydro- 

 chloric acid. The same reaction may be made with filter-paper, 

 soaked for some time in an alcoholic solution of the reagent, allowed 

 to dry, and used as test-paper. Hydrochloric acid turns this paper 

 brown, and upon heating the brown color changes to blue. (The 

 paper does not keep unchanged over a month.) 



